• starik@lemmy.today
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    7 hours ago

    Just always convert the percentage to a decimal, and it’s easy either way.

    0.06x50 is as easy as 0.5x6. They’re both just 5x6.

    All these comments like “What about 47% of 3.11?” Well, yeah, of course it’s harder to multiply two- and three-digit numbers than it is to multiply single-digit numbers.

  • stickyprimer@lemmy.world
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    15 hours ago

    Fuck. I had to calculate 4% of 7 a few minutes ago and didn’t know this. I say fuck because it wouldn’t have helped me anyway.

      • stickyprimer@lemmy.world
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        7 hours ago

        My brain was more like “Okay it’s just seven point-fours. So what’s seven fours? 28. What’s seven point-fours? 2.8. That can’t be right. Fuck. Get a calculator.

        • qarbone@lemmy.world
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          4 hours ago

          I go for finding percentage factors.

          4%? That’s just 1% * 4. 1% of 7 = 0.07 * 4 = 0.28

          14%? That’s just 10% + 1% * 4 = 0.7 + 0.07 * 4 = 0.98

          You tell it’s decimal, then I’m gonna Decimal.

  • SnarkoPolo@lemmy.world
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    15 hours ago

    True mathematics derives from established mathematical theory, not some farcical aquatic armored vehicle!

  • melsaskca@lemmy.ca
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    22 hours ago

    It was recently discovered that all AI everywhere was connected to the Panzer all along. /s

    • ColeSloth@discuss.tchncs.de
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      1 day ago

      it’s very often not useful. Like, what’s 6% of 80? See. Still hard.

      Also, with the 6% of 50 example it’s easy without using this trick.

      What’s 6% of 100? 6, right? So cut 100 in half to get to 50, and cut the 6 in half to get the 3. Cut the 50 in half again and cut the 3 in half again, and you’ll also know that 6% of 25 is 1.5.

      Which also lets you know that 6% of 75 is 4.5. the 3 from the 50, plus the 1.5 from the 25. or just know to split the difference between the 3 at 50 and the 6 at 100.

      A lot of math is just tricks for a thinking process.

      • starik@lemmy.today
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        7 hours ago

        It’s always as easy as multiplying the two numbers. Just convert the percentage to a decimal.

        0.06x80 is just as easy as 0.8x6. It’s just a matter of knowing 6x8 is 48, which quickly gets you to 4.8 here.

      • Atomic@sh.itjust.works
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        21 hours ago

        6% of 80. 1% of 80 is 0.8 0.86 is (86)/10 Which is 48/10 = 4.8

        80% of 6. I’d probably think of it as (4/5)*6 = 24/5 Which is 20/5 + 4/5 = 4 + 4/5 = 4.8

        Both are easy if you know how to visualise it. The benefit of knowing you can “reverse” it is that you can choose which method is easier for you to visualise. Which is incredibly useful for a lot of people

      • ddplf@szmer.info
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        1 day ago

        Good luck explaining your supreme methodology to anyone that isn’t a geek.

        • ColeSloth@discuss.tchncs.de
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          1 day ago

          It’s stupid simple… If you know 6% of one hundred is 6, then you should know 6% of 50 is 3. You just cut each number in half.

  • TrackinDaKraken@lemmy.world
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    2 days ago

    Let’s try this on a sale item. Hmm, let’s see, the sign says 25% off $6.99. So that’s the same as, let’s say, 7% off $25. Oh, yeah, that is much easier. /s

    • starik@lemmy.today
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      7 hours ago

      It’s always as easy as multiplying the two numbers. Obviously some pairs are easier than others. 7x25=175. Not too hard. $1.75 off.

      • LordKitsuna@lemmy.world
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        1 day ago

        I mean if you remove the word off it works. 25% off $100 is $25 100% of 25 is 25 it’s still reversible you just let the word off confuse you

        • derfunkatron@lemmy.world
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          1 day ago

          You could also make sure to carry “off” to both sides when you swap:

          25% off of $100 is 100% of $25 off

    • Jankatarch@lemmy.world
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      1 day ago

      They said the water could reach up to 50% of its 1.7 meter height before causing problems, panzer tried calculating 1.7% of 50 meters from head, this is the result.

  • kryptonianCodeMonkey@lemmy.world
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    22 hours ago

    Another counter-intuitive percentage fact: A 10 percent discount and a 10 percent fee can be calculated in either order but they don’t cancel out.

    Example, 90% of (110% of 10) = 110% of (90% of 10). But neither of those is evaluates to 10. They evaluate to 9.9.

    For any percentage X, and any base value C, (100 - X)% x ((100 + X)% x C) = (100 + X)% x ((100 - X)% x C) = (100 - (X^2/100))% x C

  • taiyang@lemmy.world
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    1 day ago

    I was waiting in a car in front of a math tutoring building and was doing the math problems advertised on their window (as one does, of course) and the 7% of 250 is indeed probably easiest as 250% of 7, aka 2.5x7, which is 17.5.

    I did it a few other ways, though. 7% of 1000 is 70, then divide by 4 for 17.5. Well, more like, divide by 2 for 35 and again for 17.5, but yeah… mental math is fun.